Interbreeding Common? Ancient Human Had Neanderthal-Like Ear

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The remains of an ancient human in China not thought to be
Neanderthal has an inner ear much like that of humans' closest
extinct relatives, according to a new study. These new findings
could be evidence of interbreeding between Neanderthals and other
species of archaic humans in China; however, the researchers say
human evolution could be more complicated than is often thought,
and the implications of the new discovery remain unclear.

Although modern humans are the only living members of the human
family tree, a number of other human lineages once lived
alongside the
ancestors of modern humans. These so-called archaic humans
included Neanderthals, the closest extinct relatives of modern
humans, who lived in Eurasia roughly between 200,000 and 30,000
years ago.

To learn more about
human evolution, scientists investigated a 100,000-year-old
human skull known as Xujiayao 15, found 35 years ago in northern
China alongside human teeth and bone fragments. At first, the
researchers thought that the skull belonged to an archaic human.
But they discovered that, anatomically, the skull — and the
fossils discovered alongside it — had characteristics
typical of a non-Neanderthal form of archaic human. [ Image
Gallery: Our Closest Human Ancestor ]

"It's clearly not modern human," said study co-author Erik
Trinkaus, an anthropologist at Washington University in St.
Louis.

However, micro-CT scans of the skull revealed an inner ear much
like those seen in
Neanderthals.

"We were very surprised," Trinkaus told Live Science. "I said,
'My God, it looks like a Neanderthal.'"

The inner ear, also known as the labyrinth, is located within the
skull's temporal bone. It contains the
cochlea, which converts sound waves into electrical signals
that are transmitted via nerves to the brain, and the
semicircular canals, which help people keep their balance as they
move. These semicircular canals are often well-preserved in
mammal skull fossils, the researchers said.

In the mid-1990s, CT scans revealed that nearly all Neanderthals
possessed a specific arrangement of their semicircular canals.
The pattern of semicircular canal sizes and positions seen in
Neanderthals was often used to set them apart from both earlier
and modern humans.

"We fully expected the scan to reveal a temporal labyrinth that
looked much like a modern human one, but what we saw was clearly
typical of a Neanderthal," Trinkaus said in a statement. In
comparison, none of the three other archaic human skulls they
analyzed from different parts of China had this type of inner
ear.

"You can't rely on one anatomical feature or one piece of DNA as
the basis for sweeping assumptions about the migrations of
hominid species from one place to another," Trinkaus said in a
statement.

Instead, "what these findings say to me are that characteristics
were probably more varied in ancient human populations than we
think," Trinkaus said. "We see characteristics mix and match in
populations across the world nowadays, and I believe that
characteristics shuffled back and forth in ancient human
populations across the landscape over centuries and millennia.
The idea of distinct, separate lineages in this time period in
human evolution is meaningless — it was much more of a labyrinth
than that."

It remains uncertain whether these differences in the inner ear
would have led to any differences in balance or agility between
modern humans and other human groups. "Eventually, someone might
sort out the biological implications of these differences, if
there are any," Trinkaus said.